Effect of Ultrasonic Shot Peening and Laser Shock Peening on the Microstructure and Microhardness of IN738LC Alloys.

IN738LC is a conventional-cast Ni-based superalloy intended for power generation and aerospace applications. Typically, ultrasonic shot peening (USP) and laser shock peening (LSP) are utilized to enhance cracking, creep, and fatigue resistance. In this study, the optimal process parameters for USP and LSP were established by observing the microstructure and measuring the microhardness of the near-surface region of IN738LC alloys.

Precipitation Evolution in the Austenitic Heat-Resistant Steel HR3C upon Creep at 700 °C and 750 °C.

HR3C (25Cr-20Ni-Nb-N) is a key material used in heat exchangers in supercritical power plants. Its creep properties and microstructural evolution has been extensively studied at or below 650 °C. The precipitation evolution in HR3C steel after creep rupture at elevated temperatures of 700 °C and 750 °C with a stress range of 70~180 MPa is characterized in this paper.

Effect of Ultrasonic Shot Peening on the Microstructure of Austenitic Stainless Steel 316 and Super Duplex Stainless Steel UNS S32750.

Shot peening for nanocrystallization of the surface region is a good way of improving corrosion-, fatigue-, and wear-resistance, etc. of metallic parts (Lu, K., 2014.

Effect of Plastic Deformation on Microstructure and Properties of 347 Austenite Steel.

A popular issue of recent scientific research is the surface modification induced by plastic deformation, such as ultrasonic shot peening (USP) on workpiece surface. USP is an efficient way to improve the mechanical behavior of specimens by inducing severe plastic deformation on their surface. Nevertheless, this surface treatment induced complex microstructural evolutions, such as grain refinement and phase transformation.

Low angle boundary migration of shot-peened pure nickel investigated by electron channeling contrast imaging and electron backscatter diffraction.

Study on recrystallization of deformed metal is important for practical industrial applications. Most of studies about recrystallization behavior focused on the migration of the high-angle grain boundaries, resulting in lack of information of the kinetics of the low angle grain boundary migration. In this study, we focused on the migration of the low angle grain boundaries during recrystallization process.

Microstructural Evolution of Super304H Upon Ultrasonic Shot Peening and Subsequent Annealing.

In this study we analyze the effect of shot peening on the microstructure and mechanical properties of Super304H, which is widely used for boiler tubes. Specimens were shot peened for 5, 10, and 15 minutes, and then heat treated at 600, 700, and 800 °C for 15 minutes. Vickers hardness was measured and the microstructure of cross sectional specimens was analyzed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM).

Effect of Shot Peening on Oxidation Behavior of SS304H Upon Long Term Steam Exposure.

Specimens of austenitic stainless steel 304H (SS304H) were shot peened and exposed to steam at 600, 650, and 700 °C for 10,000 h, 15,000, and 20,000 h. After steam exposure, un-peened SS304H has three oxide layers, Fe-O, Fe-Cr-O and Cr2O3, while shot peened specimens have an Fe-Cr-O layer, a Cr2O3 and an amorphous Fe-Si-O layer. The evolution of the oxide layers as a function of duration of steam exposure and temperature reveals that the growth of the Fe-O and the Fe-Cr-O layers is inhibited by shot peening.

Effect of the Addition of CeO or MgO on the Oxygen Carrier Capacity and Rate of Redox Reactions of NiO/FeO/AlO Oxygen Carriers.

Two compositions of mixed oxygen carriers (OCs), N1F1A1 (mole ratio of NiO to FeO is 1:1) and N1F2 (mole ratio of NiO to FeO is 1:2), were fabricated by mechanical mixing, and the effects of CeO and MgO additives on the oxygen-transfer capacity (OTC) and crystal structure were analyzed. In addition, X-ray diffractometry after the oxidation and the reduction steps was carried out to determine the reaction mechanism. Potential mixed OCs of the candidates of various OCs, such as NiO/FeO, are proposed based on the OTC and oxygen-transfer rate evaluated via X-ray diffraction (XRD) phase analysis and thermogravimetric analysis.

Characterization of Surface Modification of 347 Stainless Steel upon Shot Peening.

Plastic deformations, such as those obtained by shot peening on specimen surface, are an efficient way to improve the mechanical behavior of metals. Generally, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) are commonly used to observe the complex microstructural evolutions, such as grain refinement and phase transformation, induced by the surface treatment. In this work, the microstructure of 347 stainless steel, after ultrasonic shot peening (USP) treatments, was investigated.

Surface nanocrystallization of pure Cu induced by ultrasonic shot peening.

Peening is mainly used as a method of surface treatment for microstructural modification in order to improve surface mechanical properties. The ultrasonic shot peening (USP) technique can cause severe plastic deformation with its high strain rate on the surface of metallic parts. However, systematic studies of microstructural refinement mechanism upon plastic deformation with consideration of alloy systems are rare.

Microstructural refinement of Al-Si alloy upon ultrasonic nanocrystalline surface modification treatment.

In this work, an Al-7 wt.% Si alloy, which is widely used as the structural materials in the automotive and aerospace industries for their high specific strength, was subjected to ultrasonic nanocrystalline surface modification (UNSM) treatment. After UNSM treatment, the effect of UNSM on the microstructural evolution of both Al grain and the dispersed Si particles was studied by using scanning electron microscope (SEM) and transmission electron microscope (TEM).

Transmission electron microscopy study of microstructural properties and dislocation characterization in the GaN film grown on the cone-shaped patterned Al2O3 substrate.

Growing a GaN film on a patterned Al2O3 substrate is one of the methods of reducing threading dislocations (TDs), which can significantly deteriorate the performance of GaN-based LEDs. In this study, the microstructural details of the GaN film grown on a cone-shaped patterned Al2O3 substrate were investigated using high-resolution transmission electron microscopy and weak-beam dark-field techniques. Various defects such as misfit dislocations (MDs), recrystallized GaN (R-GaN) islands and nano-voids were observed on the patterned Al2O3 surfaces, i.

Effect of creep stress on the microstructure of 9-12% Cr steel for rotor materials.

High-chromium heat-resistant steel has been widely used as the key material to improve the condition of steam pressure and temperature in the modern high-efficiency power plants. Despite the use of the steel above 550°C for several decades, its major failure is owing to the creep fracture. In this study, the effect of creep stress on the microstructure in 9-12% Cr steel has been investigated microscopically, and it is clarified that the creep stress enhances precipitation of Laves phase and influences the lath width and dislocation density in lath interior.

Detection and determination of solute carbon in grain interior to correlate with the overall carbon content and grain size in ultra-low-carbon steel.

In this study, every effort was exerted to determine and accumulate data to correlate microstructural and compositional elements in ultra-low-carbon (ULC) steels to variation of carbon content (12-44 ppm), manganese (0.18-0.36%), and sulfur (0.

Wear behavior of Cu-Zn alloy by ultrasonic nanocrystalline surface modification.

The ultrasonic nanocrystalline surface modification (UNSM) was applied to disk specimens made of Cu-Zn alloy in order to investigate the UNSM effects under five various conditions on wear of deformation twinning. In this paper, ball-on-disk test was conducted, and the results of UNSM-treated specimens showed that surface layer dislocation density and multi-directional twins were abruptly increased, and the grain size was altered into nano scale. UNSM delivers force onto the workpiece surface 20,000 times per second with 1,000 to 4,000 contact counts per square millimeter.